An internal combustion engine is composed of many moving parts, which have to be lubricated thoroughly to minimize the mechanical friction at the time when the internal combustion engine is in operation.
The lubrication of the moving parts of a traditional compact two-stroke engine is brought about by a mixture of engine oil and engine fuel in the ratio of about 1:25. Such a lubrication system as described is defective in design in that the engine oil contained in the mixture can not be burned completely in the combustion chamber of the two-stroke engine, thereby resulting in the discharge of exhaust fume that is a potential environmental pollutant.
The lubrication system of a conventional compact four-stroke engine consists of a slinger rod, through which the engine oil kept at the bottom of the crank case is applied to the moving parts of the engine in the form of oil mist. This kind of the engine lubrication system is ineffective at best in view of the fact that certain moving parts of the engine are not lubricated at the time when the engine is tilted, as is often the case with a chain saw or hedge trimmer, and that the engine oil may be accidentally introduced into the cylinder or combustion chamber at the time when the engine is tilted, thereby resulting in the discharge of harmful exhaust fume.
An improved engine lubrication system is composed of a crank shaft on which the engine oil case is mounted. The crank shaft is provided with a slinger, through which the engine oil is applied to all moving parts of the engine in the form of oil mist. This lubrication system is limited in design in that the lubricating effect of oil mist is confined within bounds, and that the plain bearing and the overhead cam (OHC) can not be lubricated by oil mist, and further that the oil mist can be easily diminished by the engine breather, thereby resulting in an excessive consumption of engine oil.